-ի

Etymology 1
From.

Suffix

 * 1) -able

Etymology 2
From.

Etymology
From.

Etymology 1
From the or  suffix. Compare the same suffix in Sanskrit, Ancient Greek , Latin. The genitive ending may have the same origin.

Etymology 2
The genitive/dative/locative marker for i-declension is identical with the stem vowel. In Godel's words, the remaining stem, standing in contrast to the nominative/accusative singular (which lost its stem), was apt to function as a full-fledged case form. According to Godel, in the case of the i-a-declension we are dealing with a Proto-Armenian morphological innovation: the new morpheme was abstracted from the genitive/dative/locative case ending of i-stem nouns and applied to a-stem nouns, whose original endings had been lost.